1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus, and in particular to a method of processing a substrate having a silicon nitride film and a thermally-oxidized film.
2. Description of the Related Art
Wafers as substrates are known that have a thermally-oxidized film formed on a single-crystal silicon base material, and a silicon nitride (SiN) film formed on the thermally-oxidized film. For such wafers, it may be required to remove only the silicon nitride film without removing the thermally-oxidized film.
In general, as methods of removing the silicon nitride film, wet etching using hot phosphoric acid and dry etching using plasma produced from chemical compound gas are known (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2003-264183).
However, through the wet etching using hot phosphoric acid and the dry etching using plasma, it is difficult to secure the selective ratio of the silicon nitride film to the thermally-oxidized film, and as a result, not only the silicon nitride film but also the thermally-oxidized film may be etched, causing damage to the thermally-oxidized film.